In some fics, Pokey Pierce is portrayed as a Vaudeville-still stand-up comic. That may be the origin of the good ship PokeyPie. The two of them would have nothing but fun, and their parties would be amazing.

like Twilight/Dr Whooves, fans like to ship the mane 6 with a background characters, usually an alternate to the yuri onessome shippings comes from fanfictions/fanart, and i think that's where Pokepie is from